The present invention relates to a suspension device for a vehicle which is applicable to a vehicle, such as an automotive vehicle, and in particular relates to a double wishbone type of suspension device.
A conventional double wishbone type of suspension device comprises a knuckle which supports a wheel and a pair of upper-and-lower arms (an upper arm and a lower arm) which respectively support an upper portion and a lower portion of the knuckle. This type of suspension device has a defect that the upper arm is displaced forwardly and the lower arm is displaced rearwardly such that these arms are displaced in an opposite direction during braking, so that the caster rigidity of the suspension cannot be secured.
Meanwhile, resilient bushes are provided between respective vehicle-body connection portions of the upper and lower arms and a vehicle body. Herein, by designing the rubber bushes to be hard, the upper arm and the lower arm can be suppressed from being displaced in the opposite direction of the vehicle longitudinal direction, so that the caster rigidity of the suspension can be secured.
However, the above-described design causes the rubber bushes to be hard suppressing the upper arm and the lower arm from being displaced in the vehicle longitudinal direction, so that the longitudinal compliance of the suspension is suppressed improperly. Consequently, there is a defect that a longitudinal element of impact which is generated when the vehicle rides over projections is not so sufficiently absorbed by the longitudinal compliance of the suspension that the ride quality of the vehicle is deteriorated.
Japanese Patent Laid-Open Publication No. H07-246815 discloses a suspension device for a vehicle as a technology of solving the above-described defects (i.e., the technology of compatibly securing the caster rigidity and the longitudinal compliance of the suspension).
In the suspension device for the vehicle of the above-described patent document, the upper arm and the lower arm are respectively provided with two vehicle-body connection portions which are spaced apart from each other in the vehicle longitudinal direction. The two vehicle-body connection portions of the upper arm and the two vehicle-body connection portions of the lower arm are integrally connected by a facial-shaped connecting member. This connecting member suppresses the upper arm and the lower arm from being displaced in the opposite longitudinal direction, not suppressing these arms from being displaced in the same longitudinal direction, so that the caster-rigidity securement and the longitudinal-compliance securement are compatibly attained.
In the suspension device for the vehicle of the above-described patent document, however, the above-described connecting member integrally connects the vehicle-body connection portions of the upper arm and the vehicle-body connection portions of the lower arm. Therefore, the upper arm and the lower arm are not allowed to rotate in a vertical direction freely, so that the suspension function may be damaged.